The present invention relates to an automatic train control system of the type disclosed in U.S. Pat. Nos. 4,015,804; 4,023,753 and 4,266,273, all assigned to the same assignee as the present invention, whose disclosures are incorporated herein by reference, and more particularly to a facility for intermittent inductive transmission of information between guideway equipment and vehicles moving along the guideway with the energy to power the wayside equipment being supplied from this vehicle.
Such a facility is disclosed, for example, in an article by R. Beyersdorff, "Automatisches Lesen von Kennungen fur Guterwagen", Siemens Zeitschrift, November 1963, No. 11. In that prior facility, freight car numbers are transmitted from passive transponders to a trackside interrogator by means of a multifrequency code. A number of frequency generators in the transponder, which operate as frequency dividers, are activated alternately by different interrogation frequencies in accordance with the coded car number to be transmitted, and transmit simple fractions of a carrier frequency received from the interrogator back to the latter. Before being transmitted back, the signals are amplified in a transmitter amplifier. The necessary energy (DC power) is obtained by converting part of the carrier frequency received from the interrogator.
This facility is capable of transmitting 10-digit freight-car numbers to an interrogator if the speed of the cars does not exceed 100 km/h (kilometer per hour).
For transmitting information in the opposite direction, i.e., from the wayside equipment to the vehicles moving along the guideway, quite a number of other inductive facilities have been provided.
German Patent DE-AS No. 2,528,346, for example, describes a facility which uses the reaction of passive resonant circuits tuned to different frequencies on AC-powered resonant circuits of the same resonance frequency to transmit an n-out-of-m code.
While the first-described prior art facility is too slow for the speeds required in present-day transport systems and can transmit only a small amount of information, the facility described in German Patent DE-AS No. 2,528,346 is expensive and susceptible to trouble because of the many analog devices. In addition, any changes to be made in the information to be transmitted necessitates taking action in the trackside (wayside) equipment and involves alignment work. Another disadvantage lies in the use of many different frequencies.